1. Field of the Invention
This invention relates to a dental distractor and particularly to a dental distractor for correcting severe front teeth crowding and protrusion in orthodontic treatment.
2. Description of the Prior Art
Conventional orthodontic treatment for severe anterior teeth crowding or protrusion generally includes the following five steps:
1. Extracting the first premolars. PA1 2. Initial teeth leveling by using orthodontic brackets and arch wires. Depending on the alignment of teeth, this step lasts about three to six months. PA1 3. Retracting canine backward into the first premolar extraction space for anterior teeth. This step lasts about four to six months for children and seven to eight months for adults. PA1 4. Retracting anterior teeth to level the protruding teeth. This step lasts about six months. PA1 5. Fine adjustment of occlusion and tooth angulation. This step takes about three to six months. PA1 1. Putting on orthodontic brackets for initial alignment and leveling anterior teeth for one or two months. PA1 2. Extracting first premolars and putting on dental distractors to move the canines within three weeks. PA1 3. Retracting anterior teeth backward for about 4-5 months. PA1 4. Fine adjusting the occlusion and tooth angulation.
Total orthodontic treatment time will take one and a half to two years. It is too long a time for most patients. It is not esthetic to wear braces for such a long period and it is very burdensome for the patients to maintain their oral hygiene as well. It also is very inconvenient and time-consuming for the patients to visit orthodontist's office over such a long period. Two major steps make the period of orthodontic treatment long. They are the step 3 (canine retraction) and step 4 (anterior retraction), which take a whole year in total.
FIGS. 1 and 2 show a conventional method for canine reaction after first premolar extraction with an elastic power chain. The first molar is engaged with a molar band 12 and a bracket 121 welded on the buccal surface thereof. The canine 3 is engaged with a canine band 32 and a bracket 321 welded on the buccal surface thereof. An elastic power chain 2 is engaged between the brackets 121 and 321. The elastic power chain 2 is made of synthetic rubber formed in a chain manner including a plurality of loops 21. The chain is cut to a length desired and has the two end loops engaging respectively with the brackets. Through the elastic force of the elastic power chain 2, the canine 3 may be pulled gradually toward the first molar 2 and a space being left behind the canine. The rubber of the power chain 2 tends to lose elasticity after soaking in saliva for a period of time. It usually takes more than six months to retract a canine into a desirable position (i.e., moving the canine rearward for 4-5 mm). It takes too much time and prolongs the total treatment time.
FIG. 3 illustrates another conventional method for canine retraction disclosed in U.S. Pat. No. 5,873,715 which is disclosed by the same inventor of the present invention. The method illustrated in U.S. Pat. No. 5,873,715 uses a dental distractor 4. The dental distractor 4 includes a distractor head 41, a movable joint 42 and a screw 43. There is a molar band 121a mounted on the first molar 1. The molar band 12a has buccal sheaths 121a welded on buccal surface. The buccal sheaths 121a have two spaced cylindrical bores located therein. The canine 3 has a canine band 32a mounted thereon. On the buccal surface of the band 32a, there is a reversed U-shaped hook 321a fixed thereon.
Referring to FIGS. 3 and 4, the distractor head 41 includes an engaging end 411 which is substantially a C-shaped bar. The engaging end 411 has an upper bar 4114 which has two legs 41142 engageable with the cylindrical bores of the buccal sheaths 121a. The engaging end 411 further has a lower bar 4112 connecting with one end of a sliding bar 415. A screw seat 413 is fixed on the sliding bar 415 and has a first screw bore 4132 engageable with a screw bar 432.
Referring to FIG. 5, the movable joint 42 includes a connecting screw 421 with a slot 4212 and a cap 4213. The cap 4213 is to secure the hook 321a in the connecting screw 421. There is a second screw bore 423 in the movable joint 42 enagageable with a screw bar 432 of the screw 43 and a sliding bore 425. The sliding bar 415 slidably runs through the sliding bore 425. The screw 43 has a screw head 434 at one end thereof.
When a patient is undergoing rapid orthodontic treatment for correcting severe anterior crowding or protrusion, the canine 3 has to be moved backward with the distractor immediately after the first premolar extraction and before the new alveolar bone is generated. The molar band 12a is mounted on the first molar 1 and the canine band 32a is mounted on the canine 3 before the first premolar extraction. Immediately after the first premolar extraction, the distractor head 41 is mounted on the molar band 12a by engaging the legs 41142 into the buccal sheath 121a. The movable joint 42 is engaged with the canine band 32a by inserting the hook 321a into the slot 4212. Then the screw seat 413 is engaged with the movable joint 42 by turning the screw head 434. For each turn or a fractional turn, the screw head 434 will drive the movable joint 42 back a definite distance toward the screw seat 413, thus achieve the object of moving the canine 3 rapidly. The distractor of this invention may be made of high strength alloy with stable property and bio-compatibility.
By following orthodontist's instructions, patients may turn the screw head 434 easily by using a simple tool without going to orthodontist's office. The force generating by the screw 43 and the movable joint 42 is more effective than the elastic power chain.
The following is the general procedures of using this method to perform rapid orthodontic tooth movement:
Although the second method (i.e., U.S. Pat. No. 5,873,715) disclosed above may speed up orthodontic treatment, it has the problem of having too complicated and too bulky a structure. It is particularly annoying to put it in the month which is delicate and sensitive. It is prone to hurt mucous membranes and even causes oral ulcers.